This invention relates to a 4-cycle engine for vehicles, and more particularly to a secondary air introducing device in such an engine.
In a conventional secondary air introducing device of this type, a secondary air introducing hole is formed in the side wall of a cylinder of an engine in such a manner that it is located near the bottom dead center of the piston in the cylinder and is opened and closed by the piston (cf. Japanese Utility Model Publication No. 16166/1972.) In general, the secondary air introducing hole is coupled to a air source such as an air pump which is operated in association with the engine, so that the compressed air is introduced into the cylinder. In this case, the engine suffers a loss of output power because of the pump, and the mechanism of the engine is liable to be intricate in order to operate the pump. Introduction of the compressed air is effective in purifying the exhaust gas, but it is not always effective in increasing the output power of the engine.
In the case of employing the air source such as an air pump, the amount of air introduced into the cylinder, i.e., the amount of secondary air should be controlled according to variations in load of the engine. In this connection, it is desirable that means for controlling the amount of secondary air is such that the power loss of the engine is minimized.